The present invention relates to specific photochromic pyran compounds and their use in synthetic resin objects (i.e., plastic objects) of all types, especially for ophthalmic applications. In particular, the present invention relates to spiro compounds having a fluorene structure derived from naphthopyrans, which are known as spirofluorenopyrans. According to the invention, introducing, respectively, only one strongly electron donating or withdrawing group at specific positions in the periphery of the pyran dye yields photochromic compounds that in the excited state are distinguished by an expanded color spectrum, i.e., by a hypsochromic or bathochromic shift of the longest-wave absorption maximum. At the same time, these compounds offer comparably good bleaching or fade rates and good performance in the durability test.
Various classes of dyes that reversibly change their color when irradiated with light of certain wavelengths, particularly sunlight, are known in the art. This is due to the fact that these dye molecules change into an excited colored state when supplied with energy in the form of light. When the energy supply is interrupted, they leave this state again and return to their colorless or at least hardly colored normal state. These photochromic dyes include, for instance, the naphthopyrans, which have already been described in the prior art with various substituents.
Pyrans, especially naphthopyrans and larger ring systems derived therefrom, are photochromic compounds that even today are the subject of intensive investigations. Although a patent application was filed for them as early as 1966 (U.S. Pat. No. 3,567,605), it was not until the nineties that compounds that appeared suitable for use in eyeglasses were developed.
The prior art 2H-naphthopyrans derived from 1-naphthols as well as their higher analogue derivatives obtained by annellation are connected with drawbacks, however, and when used in sunglasses, substantially affect the wearing comfort of the glasses wearer. On the one hand, the prior art dyes frequently do not have sufficiently long-wave absorption in the excited as well as in the unexcited state. This causes problems also in combinations with other photochromic dyes. On the other hand, they are also often excessively temperature sensitive with respect to darkening, and brightening is simultaneously too slow. In addition, the described dyes have an insufficiently long service life. Consequently, this type of sunglasses is not adequately durable. The latter is noticeable in their rapidly deteriorating performance and/or strong yellowing.
By introducing a spirofluorene skeleton as described in German patent applications DE 198 24 278 or DE 199 02 771, photochromic compounds with correspondingly improved properties have been provided. However, their longest-wave absorption maximum in the excited state lies in a very narrow wavelength range of 570 nm to 620 nm. As a result, for instance, green sunglasses can be obtained only by mixing different photochromic dyes. Since the kinetics of the individual photochromic dyes, however, cannot be completely tuned or matched to one another in these dye mixtures, the occurrence of color differences during darkening and bleaching is unavoidable.
It is an object of the invention to provide novel photochromic pyrans, which are to be distinguished by a broader color spectrum in the excited state than is available in prior art compounds.
Another object of the invention is to provide photochromic compounds which have comparably good kinetic properties.
A specific object of the invention is to provide photochromic compounds which combine rapid bleaching rate with excellent durability.
A further object of the invention is to provide photochromic compounds with which It is possible to obtain green sunglasses by using them alone.
These and other objects are achieved in accordance with the invention by providing a photochromic pyran compound corresponding to formula I: 
wherein
R1, R2, R3 and R4 are each independently selected from the group xcex1 consisting of the subgroups A, Axe2x80x2 and Axe2x80x3,
in which
subgroup A consists of hydrogen, (C1-C6) alkyl, (C1-C6) alkoxy, (C3-C7) cycloalkyl which may include one or more heteroatoms, aryl, heteroaryl, benzyl, hydroxy, bromine, chlorine, and fluorine;
in subgroup Axe2x80x2, R1 and R2 or R3 and R4 respectively form an xe2x80x94Oxe2x80x94(CH2)nxe2x80x94Oxe2x80x94 group bound to the aromatic ring, wherein n=1 or 2, and
subgroup Axe2x80x3 consists of strongly electron withdrawing groups selected from the group consisting of xe2x80x94CF3, xe2x80x94NO2, xe2x80x94CN and xe2x80x94SO2R5, wherein R5 is selected from subgroup A, and strongly electron donating groups selected from the group consisting of thio(C1-C6) alkyl, thiophenyl, thiobenzyl, thiomorpholinyl, morpholinyl, piperidinyl, an azacycloheptanyl, piperazinyl, pyrrolidinyl, pyrazolidinyl and unsubstituted, monosubstituted or disubstituted amino, wherein the amine substituents are selected from the group consisting of (C1-C6) alkyl, (C3-C7) cycloalkyl, phenyl and benzyl,
with the proviso that R1 and R2 are bound either directly to the benzopyran unit of formula (I) or via an aromatic or heteroaromatic ring system annellated to the benzopyran unit to form a corresponding naphthopyran unit, and
with the further proviso that of R1 and R2, and of R3 and R4, respectively, only one member of each pair is a strongly electron withdrawing group or a strongly electron donating group selected from subgroup Axe2x80x3,
G including the central Spiro carbon atom represents a saturated or unsaturated ring with 5 to 8 carbon atoms of which at most one may be replaced with a hetero moiety selected from the group consisting of O, S and NR5, where R5 has the meaning given above
wherein at least one aromatic or heteroaromatic ring system selected from the group E is annellated to the ring G, wherein group E consists of benzene, naphthalene, phenanthrene, pyridine, quinoline, furan, thiophene, pyrrole, benzofuran, benzothiophene, indole and carbazole, and wherein the ring system optionally may have one or more substituents from the group xcex1 defined above;
B and Bxe2x80x2 are independently selected from one of the groups a), b), c) and d) wherein
group a) consists of monosubstituted, disubstituted and trisubstituted aryl selected from the group consisting of phenyl and naphthyl;
group b) consists of unsubstituted, monosubstituted and disubstituted heteroaryl selected from the group consisting of pyridyl, furanyl, benzofuran-2-yl, benzofuran-3-yl, thienyl, benzothieno-2-yl, benzothieno-3-yl or julodinyl;
wherein the substituents of the aryl or heteroaryl in a) and b) are selected from the group consisting of hydroxy, amino, mono(C1-C6) alkylamino, di(C1-C6) alkylamino, mono- and diphenylamino unsubstituted, monosubstituted or disubstituted on the phenyl ring, piperidinyl, morpholinyl, carbazolyl, unsubstituted, monosubstituted and disubstituted pyrryl, (C1-C6) alkyl, (C1-C6) alkoxy, bromine, chlorine, and fluorine, wherein the substituents of the phenyl or pyrryl are selected from the group consisting of (C1-C6) alkyl, (C1-C6) alkoxy, bromine, chlorine, and fluorine;
group c) consists of structural units having the formulas (V) or (W): 
xe2x80x83wherein Y and Z are independently selected from the group consisting of O, S, CH, CH2 or NR9, wherein R9 is selected from the group D consisting of (C1-C6) alkyl, (C1-C6) acyl, phenyl and hydrogen; R6 and R7 independently represent hydrogen or (C1-C6) alkyl; R8 is a substituent selected from the subgroup A defined above, and n is 0, 1, 2 or 3;
with the proviso that if Y in formula (V) is NR9, Z is carbon, and
in group d) B and Bxe2x80x2 together form an unsubstituted, monosubstituted or disubstituted fluorene-9-ylidene radical or a saturated hydrocarbon radical, which is C3-C12 spiro-monocyclic, C7-C12 spiro-bicyclic or C7-C12 spiro-tricyclic, wherein the fluorene substituents are selected from the subgroup A.